Radio Frequency Identification (RFID) has existed for several decades now, and has experienced many different standards, applications, and interoperability and compatibility issues. However, the RFID EPC Gen2 standard, introduced in 2004, has become a unified standard across the industry.
RFID uses modulated backscatter. Modulated backscatter is a technique where a continuous wave radio frequency signal is essentially turned on and off (modulated) and reflected back to the receiver. The turning on/off is simply switching an RF switch which does not require very much power. It is similar to a flashlight generating the light (expensive), someone else flipping a mirror back and forth (inexpensive switch), and a third device looking at the reflections of the mirror to receive the message.
FIG. 1 illustrates a backscatter communication system. Referring to FIG. 1, device 1 generates the continuous wave signal. Device 2 is the tag, which modulates the signal with the intended data. Device 3 is the backscatter receiver, which reads the modulated signal and demodulates it into the original message from Device 2. In RFID, devices 1 and 3 are combined into the same physical device, but this is not required.
A key feature of RFID is that it is batteryless. An RFID tag harvests the incident energy that it is backscattering for communication, converts the energy to DC power, and stores the energy in a capacitor for use by the tag. In this way, there are no batteries required, and the tag functions as long as there is sufficient incident RF energy.
Bluetooth is a standard wireless communication interface that is over 10 years old. Bluetooth communicates in the 2.4 GHz ISM frequency band. Traditionally, WiFi 802.11 occupies much of this space, so Bluetooth has been designed to communicate in frequency sub-bands where WiFi is known to be less prevalent, and Bluetooth receivers are also designed to be sensitive to slight perturbations on the incoming signals due to competing RF communications standards in this space.
Bluetooth Version 4.0 is also known as Bluetooth Low Energy (BLE) or Bluetooth Smart. BLE takes the low-power feature of Bluetooth to a new level by reducing the pairing and communication requirements, therefore reducing the time the radio must be on. This new low-power standard has made BLE the wireless radio interface of choice for “Internet of Things” type communication systems. Battery powered sensor tags that communicate via BLE are very common. Moreover, BLE radio receivers are available on a wide variety of platforms that people carry around with them every day, including smartphones and tablets. Therefore, anyone with one of these devices can read devices which transmit BLE messages.
Advertising Packets
Any device can transmit BLE advertising packets, without pairing with a reading device. Advertising packets are only, and always, sent on all three of channels 37, 38, and 39. As a result, many sensor tags use advertising packets to transmit their sensed data, because the sensor can easily create such a packet and send it and shut down quickly, minimizing expensive radio-on time for the sensor tag. Meanwhile, receivers (actual BLE radio nodes) receive the advertisement, and appropriate software on the receiver (e.g., cellphone), can then act upon it.
Computational RFID
Computational RFID is a relatively new enhancement to the types of RFID devices that are supported. Traditionally, the data encoded into an RFID tag are permanently fixed bits that can represent an ID field and any other fixed distinguishing identifiers of the tag.
Computational RFID creates an RFID data field that can be changed. The data payload in computational RFID can include, for example, sensor data (temperature, humidity, pressure, etc.). The payload can be configured to include the current temperature, and the CRC checksum can be updated to account for the different bit fields. Computational RFID is gaining popularity because of this enhanced capability because it is more flexible than a fixed ID tag.
Computational Bluetooth
Computational Bluetooth expands upon BLE by proposing a practical system implementation of the same, and due to the nature of embedding sensed data in the payload, and using backscatter communications, it is similar to computational RFID.